The U.S. Postal Service uses primarily scanning apparatus to read coded information imprinted on envelopes and packages. In addition to the bar code scanner, the Postal Service also uses alphanumeric optical character readers. While these devices can read both letters and numerals, they also can read bar codes.
A basic requirement for this sensing apparatus is that there be at least a predetermined contrast between the envelope paper or background and the ink which constitutes the bar code or other information. The optimum condition would require the maximum reflectivity from the paper and the minimum reflectivity from the printed material thereon. The reflectance of the paper and of the ink are parameters which are used to calculate the print reflectance difference (PRD) and print contrast ratio (PCR). The PRD and the PCR for a piece of mail then must meet postal service standards or it will be unacceptable for automatic handling.
A laboratory spectrophotometer can be used to evaluate the reflectance of the paper and of the ink. Conventional laboratory spectrophotometers, however, are large pieces of equipment and, therefore, not portable. In addition, they are quite expensive in that they are intended normally to perform a variety of functions not necessary to or not related to the requirements for an envelope reflectance meter. In addition, a spectrophotometer will produce a reading of reflectance from the paper and reflectance from the ink. However, a spectrophotometer does not calculate the PRD and PCR required to evaluate the object against U.S. Postal Service standards. Therefore, the technician would have to manually calculate the standard values if using a laboratory spectrophotometer.
There is a portable unit available manufactured by Photographic Sciences, Inc. which will read reflectance and display the calculation of the PRD and PCR automatically. The device consists of two units interconnected by a cable, and the operator takes readings with a microscope-type eyepiece in one unit and the display is in the other unit.
There is, therefore, a need for a lightweight, portable device for use by the U.S. Postal Service for evaluating reflectance, which can be used by a relatively untrained operator, and which is accurate and does not require frequent calibrations.